Just two, me and my passenger.

I've given it some thought and assuming that my calculations of distance are about right, and my fuel consumption is somewhere between 9-10 KM/L for the L200, then I think the low numbers could be attested to my driving.

It was my first time driving an awfully slow car on a long-distance trip, and I'm used to traveling at 100-140 kph on the highway if the traffic allows. I didn't have a working speedometer during the trip, but seeing as I was able to overtake most cars on the highway (the trip up is a different story, the old pickup took forever to pass a car uphill, it was almost dangerous), I guess I was also traveling at around 100-120 kph.

This may have put so much stress on the engine (no tachometer but I have this feeling I was near the redline since I wasn't increasing in speed anymore even if I floored it), that even if the engine is inherently efficient, when at 100% load, it gobbles diesel as well. Driving at those speeds with a 2-liter vehicle on the other hand isn't as stressful to the engine, which may explain why the fuel consumption is better.

This is of course, just a theory, and I just based it on the Top Gear feature wherein an M3 had better mileage than a Prius around the track, with both cars going at the fastest the Prius can go.